The present invention relates to an electronic visual display test apparatus, and more particularly it relates to a test instrument providing a visual motion display which becomes stationary when the frequency of an electronic timepiece is adjusted to coincide with a calibration frequency generated within the apparatus.
Electronic timepieces, particularly digital-display electronic watches, utilize either continuous or intermittent digital time displays driven by a time signal. This signal is derived by frequency divider circuits driven from a time-base signal generator controlled by a quartz crystal. The crystal frequency may be at any one of a number of frequencies. Typically, frequencies utilized by watch designers are selected to coincide with an integral power of the base two. For instance, one commonly used frequency is 32,768 hertz (or 2.sup.15 hz) and another is 4,194,304 hertz (or 2.sup.22 hz). The selection of a time base frequency must take into account two factors: one, the universal time period for all timepieces is one second, and two, crystal tolerances are best controlled in a range from about 2.sup.15 to 2.sup.22 hz.
Certain crystalline materials when subjected to the influence of an electric field, tend to vibrate at a periodic rate, commonly known as the resonant frequency. These vibrations have long been used in crystal oscillator circuits to control the frequency of the oscillator because the crystal presents a very low impedance feedback path to the oscillator at precisely its resonant frequency. The intrinsic resonant frequency of a crystal typically varies slightly from crystal to crystal because of a number of factors which cannot be completely controlled such as physical size. However, the resonant frequency of any crystal can be made to vary slightly by addition and subtraction of capacitance. Consequently, electronic timepieces using time-base crystal oscillators routinely provide a small trimmer capacitor to enable tuning of the crystal to a precise desired frequency which can be used to control circuitry to drive an accurate time display. The present invention provides a visual tuning-aid that makes possible a rapid and precise alignment of the trimmer capacitor of an electronic timepiece, such as a digital wristwatch.
Heretofore, adjustment of the trimmer capacitor was accomplished primarily with a precision digital frequency counter capable of displaying at least five and sometimes many more digits of different numbers representing the frequency or period of the time-base signal generator of a timepiece to be aligned. Use of those frequency counters, especially in production line situation resulted in eyestrain and undue operator fatigue. Impermissable calibration errors naturally resulted. In addition, each digital frequency counter tended to be very expensive because of the substantial costs of precision master oscillators which were required and contained in each such counter. In addition, reading the required digits of such a counter caused the operator to spend a substantial amount of time for each timepiece undergoing calibration. Thus, production rates were slow because of delays at the calibration station, a drawback only overcome by increasing the number of such stations. These and other disadvantages are overcome by the present invention.
In use, electronic timepieces from time to time require readjustment of the frequency generator element. Typically, such recalibration is required after the timepiece is dropped or otherwise jarred or subjected to severe mechanical shock. Such shock tends to realign the quartz crystal or causes it to vibrate at a slightly different resonant frequency which has thereby necessitated recalibration. Thus, in addition to an initial precise calibration, the trimmer capacitor provides a recalibration mechanism for setting the crystal oscillator of electronic timepieces from time to time as the need arises. It is consequently important that the trimmer capacitor provide a sufficient tuning range on both sides of the precisely desired frequency so that subsequent adjustments can be performed either up or down as may be required in a particular timepiece. Heretofore, as with the initial calibration of the trimmer, its recalibration was also accomplished with a digital counter having the drawbacks already mentioned. This problem is also overcome by the present invention.
With greatly increased production and use of electronic timepieces having trimmer capacitors for precise calibration, a need arose for a simple, inexpensive and reliable calibration tool that field repair stations and jewelers can utilize for field recalibration of electronic timepieces. Heretofore, no simple test apparatus was available to field stations and jewelers. Again, the apparatus of the present invention fills that need.
In view of the foregoing, it is an object of the present invention to provide a simple visual indication system enabling rapid, precise calibration of electronic timepieces to a correct frequency as well as determination of the tuning range of such timepieces.
Another object of the present invention is to provide a tuning-aid system for electronic timepieces in which an unmistakable moving visual display ceases to move when the timepiece is adjusted precisely to the correct frequency.
It is a further object of the present invention to provide a visual tuning-aid system for electronic timepieces which may supply multiple tuning stations with a calibration frequency signal which is closely set to a reference signal broadcast by the National Bureau of Standards or other primary frequency standard.
Yet another object of the present invention is to provide a simple and inexpensive visual tuning-aid test instrument for use by electronic timepiece service stations and jewelers for field calibration of electronic timepieces to a correct frequency.